This invention relates to a method of manufacturing a photographic reflecting support. Herein, the photographic reflecting support means a support for a photographic material, which is so-called a photographic printing paper, capable of serving to directly observing a photographic image with reflected light.
Heretofore, as conventional supports of reflecting photographic materials, a polyethylene-coated paper has generally been used and to which a polyethylene layer having been prepared by blending with a white pigment or the like has been provided on the base paper made of pulp. However, the use of such polyethylene-coated paper has usually impaired the brightness, sharpness and consequent overall beauties of the resulting photographic image because of its rough and wavy glossy surface caused by the uneven surface of the original paper. Furthermore, since such base paper is covered with water-impermeable polyethylene film on both surfaces but not on cut sections, such processing solutions as a developer and the like possibly intrude through these sections into the entity of paper, and its possible migration to photographic layers during aging causes seriously adverse effects to the photographic image.
As means to resolve such problems of conventional supporting material, some techniques have been proposed with use of only a thermoplastic film instead of the base paper.
For example, certain techniques to fill polystyrene film with white pigment have been disclosed in Japanese Patent O.P.I. Publication No. 114921/1974, and Japanese Patent Examined Publication No. 5104/1980, but such a film still has a drawback to be hard and brittle. From the viewpoint of physical properties such as the mechanical strength of film, such polyester resins as polyethylene terephthalate appear to be better to use; accordingly, techniques to use polyester resins also have been disclosed, for example, in British Patent Nos. 1,563,591 and 1,563,592, in which the material of polyester resin was blended with barium sulfate, and then stretched; furthermore, in Japanese Patent Examined Publication No. 4901/1981, a technique was disclosed with the combination use of barium sulfate and titanium oxide.
In order to use a film made from polyester resin as a photographic reflecting support, its whole visible range transmittance is necessary to be not more than 20%, and its thickness is desirable to be 40 to 300 .mu.m. A support which meets such conditions may be generally manufactured in processes including melting, extruded through a slit die, and quenched with a rotating drum and biaxially stretching of thermoplastic resin mainly composed of polyester resin which contains not less than 10 weight % of dispersed white inorganic pigment. However, sheet materials which are made by melting, extruding and cooling of the thermoplastic resin containing such a large amount of white inorganic pigment is too brittle to be submitted to a steady stretching process without frequent ruptures, to obtain a film with a sufficient toughness. Although, as a biaxially stretching process, the means to monoaxially stretch the material lengthwise and then widthwise or in the converse order may be generally advantageous in the viewpoint of production cost, it has a serious drawback that the material is readily ruptured particularly on the second, transverse stretching step, and thus it is unsuitable for securing a long sized supporting product. Some techniques of simultaneously biaxial stretching also have a similar drawback of rupture.
The invention has been made to resolve the above drawback, and its object is therefore to present a steady manufacturing method of a photographic reflecting support with a sufficient strength, which is composed of thermoplastic resin that mainly comprises polyester resin and contains not less than 10 weight % of dispersed white inorganic pigment.